US2967043A

US2967043A - Blades and blade mounting assemblies for turbines and axial flow compressors

Info

Publication number: US2967043A
Application number: US695841A
Authority: US
Inventors: Leonard J Dennis
Original assignee: D Napier and Son Ltd
Current assignee: Napier Turbochargers Ltd
Priority date: 1956-11-30
Filing date: 1957-11-12
Publication date: 1961-01-03
Anticipated expiration: 1978-01-03
Also published as: NL222612A; CH345903A; NL102164C; GB822067A; BE562857A; FR1188652A

Description

Jan. 3, 1.961 L. J. DENNIS 2,967,043

BLADES AND BLADE MOUNTING ASSEMBLIES FOR TURBINES AND AXIAL FLOW COMPRESSORS Filed Nov. 12, 1957 2 Sheets-Sheet 1' (o m I4 0 If I!!! 4 If I INVENTOE LEONARD J DENms,

ATTORNEY L. J- DENNIS BLADES AND BLADE-MOUNTING ASSEMBLIES FOR TURBINES AND AXIAL FLOW COMPRESSORS Filed NOV. 12, 1957 Jan. 3 11961 2 Sheets-Sheet 2 INVENTOR LEONARD J. DENNIS ATTQRNEY" United States Patent BLADES AND BLADE MOUNTING ASSEMBLIES TURBINES AND AXIAL FLOW COMPRES- Leonard J. Dennis, Carpenders Park, England, assignor to D. Napier & Sons Limited, London, England, a British company Filed Nov. 12, 1957, Ser. No. 695,841

Claims priority, application Great Britain Nov. 30, 1956 4 Claims. (Cl. 253--77) This invention relates to blades and blade mounting assemblies for turbines or axial flow compressors, of the kind in which the mounting is provided with a ring of substantially axial grooves to receive the blade roots and each blade is made of sheet metal or tube manipulated into hollow aerofoil form.

In practically all hollow blades manipulated from sheet metal or tube there is a transition zone between the actual aerofoil zone and the root zone that lies within the groove in the blade mounting. Since in the transition zone the blade does not have the required aerodynamic form of the aerofoil zone it is a common practice to provide the blades with platform members which abut between the blades. The platform members afford a barrier between the transition zones and the flow channels between the blades in the aerofoil zones. In conventional forms of hollow blades the provision of a platform member on each blade complicates the construction of the blade and increases its weight, thereby increasing the centrifugal loading that has to be resisted by the blade root in the case of a rotor blade.

In a blade and blade mounting assembly according to the present invention the mounting is provided with a ring of substantially axial grooves to receive the blade roots, each blade is made of sheet metal or tube manipulated into hollow aerofoil form with two root tongues, one tongue extending from the concave flank and fitting in one of the said grooves in the mounting together with the root tongue extending from the convex flank of the adjacent blade on one side, and the other tongue extending from the convex flank and fitting in the adjacent groove together with the root tongue extending from the concave flank of the adjacent blade on the other side, and there are platform members between adjacent blades each platform member having a projection which enters the groove occupied by root tongues of the blades on each side of it.

This arrangement enables the root tongues to be spaced a substantial distance apart to lend lateral rigidity to the blades while the grooves can be made relatively narrow, and it also permits the provision of platform members which are separate from the blades and which therefore do not increase the weight or complicate the construction of the blades.

In one form of the invention each platform member is approximately T- or L-shaped in cross-section, the stem of the T or L constituting the projection which enters the groove and the cross piece of the T or L constituting a barrier which extends between adjacent blades. In such an arrangement, the side walls of each groove may be undercut, the root tongues being formed to extend into these undercut portions of the groove and the projection of the platform member having an enlarged and the width of which is wider than the gap between the root tongues at the mouth of the groove. Thus, in the case of a turbine or compressor rotor, centrifugal forces acting on the platform member cannot cause it to fly out of the groove since it will be retained therein by the enlarged end of the projection. Moreover, the projection will also help to retain the root tongues of the blades in the groove.

If desired, a retaining key may be inserted into each groove to wedge the two root tongues and the platform projection firmly in the groove.

At least one root tongue of each blade, in the transi tion zone between the aerofoil zone and the root zone of the blade, may be provided with a resilient lug engaging an adjacent platform member and serving to modify the vibration characteristics of the blade.

In another form of the invention a tubular ferrule extends transversely through each blade in the transition zone between the aerofoil zone and the root zone, and at least one lacing wire passes through these ferrules and through the platform members, which wire serves to modify the vibration characteristics of the blades. It is known that wire lacing has an advantageous effect on blade vibration characteristics, but it has hitherto been the customary practice to thread such lacing wires through the aerofoil portions of the blades. This has the disadvantage that the lacing wires are in the gas stream. By putting the lacing wire in the transition zone it is removed from the gas stream. The ferrules reduce wear in the thin metal of the blades where the lacing wire passes through the blades, and in the wire itself.

One form of blade and blade mounting assembly embodying the invention, and two modifications thereof, will now be described by way of example with reference to the accompanying drawings in which:

Figure l is an exploded perspective view of a fragment of a turbine rotor embodying the invention, showing part of the turbine disc, two adjacent turbine blades, a platform member shared by these two blades, and a retaining key for these parts;

Figure 2 is a fragmentary cross-section of the assembled turbine rotor of Figure l on a larger scale;

Figure 3 is a fragmentary cross-section similar to Figure 2 showing a modification;

Figure 4 is a fragmentary cross-section similar to Figure 2 showing another modification; and

Figure 5 is a developed circumferential section taken on the line V-V in Figure 4.

Referring to Figures 1 and 2 of the drawings, the turbine rotor consists of a turbine disc 10 having straight axial grooves 11 formed around its periphery. Each groove 11 is undercut so that in cross-section it has a circular inner portion 12 communicating with the periphery of the turbine disc through a relatively narrow mouth 13. Thus the side walls 51, 52 of each groove 11 have undercut lower portions defined by said circular inner portion 12, and overhanging

upper extremities

53, 54 defining said mouth13.

Each blade is made of a single piece of sheet metal or tube manipulated into appropriate form, and consists of an aerofoil zone 14 having a convex flank 15 and a concave flank 16, and, extending from the flanks,

root tongues

17 and 18 respectively. Each root tongue comprises a transition zone 19 and terminates in a root zone 20. In the root zone the extremities of the root tongues are shaped to fit in the grooves 11, one tongue 17 in one groove and the other tongue 18 in the adjacent groove. The

root tongues

17 and 18 are splayed outwardly so as to provide a considerably wider base for the blade than is obtained in conventional constructions in which the root portion of a blade is received in one groove in the rotor.

Disposed between and shared by adjacent blades there are separate platform members 21. Each platform member is approximately T-shaped in cross-section for the major portion of its length, except at and near its centre where it is approximately L-shaped as shown in Figure 2,

this change in section being due to the curved form of the top portion or cross-piece 55 of the platform mem her. This top portion has a convex top edge 22 and a concave top edge 23. The convex top edge 22 lies against the concave flank 16 of the blade on one side of the platform member, at the level of the junction between the aerofoil zone 14 and the transition zone 19, and the concave top edge 23 lies against the convex flank 15 of the blade on the other side, also at the level of the junction between the aerofoil and transition zones. A perforated projection 24 which constitutes the stem of the T or L in cross-section is straight to conform to the groove 11 in which it is to be inserted. The foot of the projection 24 is in the form of a semi-cylindrical bulge which lies within the circular undercut portion ,12 of the appropriate groove 11 in the assembled rotor,

with the extremities of the

root tongues

17 and 18 which fit into this groove lying one on each side of it. The thickness of the projection 24 above the bulge 25 is such that the projection will just pass through the gap between the

root tongues

17 and 18 in the mouth 13 of the groove 11 At the ends of the platform member 21 there are

end walls

26 and 27 respectively, which walls blank off the, ends of the spaces between the blades in the transition zone 1 Toassemble the rotor, the blades and platform members are first assembled into a ring on a suitable jig and the rotor disc is then applied in an axial direction so that the foot of the projection of each platform member and the adjacent root tongues of the blades on each side together enter one of the grooves in the rotor. Semicylindrical keys 28 are then driven into thesemi-cylindrical spaces left in the grooves between the extremities of the root tongues therein and beneath the bulges 25 of the platform members, so as firmly to wedge the platform members and the root tongues in the grooves.

Referring now .to the modification shown in Figure 3, a resilient lug 30 is welded to the root tongue 18 of each blade. Each lug is approximately L-shaped in crosssection, one limb 31 having a hole 32 in it through which the weld metal 33 isapplied, and the other limb 34 being doubled over to press against the underside of the top of they adjacent platform member 21. There is an aperture 35 in the bend between the two limbs of the lug,

to increase the resilience. of the lug. The limb 34 of the lug, by resiliently pressing against the platform member 21, provides frictional restraint against transverse vibrations of the blade and thereby modifies favourably thevibration characteristics of the blade.

Referring to the modification shown in Figures 4 and 5, a ferrule 37 extends through apertures in the

root tongues

17 and 18 of each blade and is welded or brazed in position. The bore of. the ferrule is reduced atv 38 as shown in Figure 5, and, a lacing wire 39 is threaded circumferentially through the bores of all the ferrules, this wire being a snug fit in the reduced bores 38.. At intervals, in its length the wire 39 may be bulged as shown at 40 or otherwise deformed in order to locate it circumferentially. The lacing wire passes through the transition zone 19 of each blade and through one of the. perforations 41 in the projection 24 of each platform member. The lacing wire-favourably modifies the vibration characteristics of the blades by applying frictional restraint against lateral flutter. The ferrules prevent the lacing wire from causing wear on the root tongues where the wire passes through the latter.

Since the present invention permits wide spacing of 4 the

root tongues

17 and 18 of each blade, apertures such as 56 may be provided between these tongues for the admission and/or discharge of cooling medium if it is desired to circulate this through the interior of the hollow blades.

What I claim as my invention and desire to secure by Letters Patent is:

l. A blade and blade mounting assembly comprising a plurality of blades each made of thin metal and having an aero'foil portion with 'a convex flank and a concave flank, a first root tongue extending from said convex flank and a second root tongue extending from said concave flank, said blade mounting having grooves therein including side walls defining a plurality of substantially axial blade root supports, said side walls having undercut lower portions and overhanging upper extremities defining a mouth to each of said grooves, platform membersdisposed between adjacent blades, each platform member having a projection received in one of said grooves which groove also receives said first root tongue of a blade adjacent one side of said platform member and said second root tongue of a blade adjacent the opposite side of said platform member, said first and second root tongues extending through said mouth into said undercut lower portions and fitting against said groove side walls with a gap between said root tongues at said mouth, said projection of said platform member extending through said gap and having an enlarged inner end the width of which is wider than said gap and which fits between said first and second root tongues, and a retaining key in each groove engaging said projection beneath said enlarged inner end and urging said projection toward said mouth to wedge said first and second root tongues between said enlarged inner end thereof and said overhanging upper extremities of said groove side walls.

2. A blade and blade mounting assembly according to claim 1 in which each platform member has a crosspiece constituting a transverse barrier extending from the convex flank of said blade on one side of said plat- ;form member to the concave flank of said blade on the opposite side of said platform member.

3. A blade and blade mounting assembly according to claim 1 in which each. root tongue has a root zone which lies within one of saidgrooves and a transition zone extending from said root zone to said aerofoil portion, and a resilient lug is provided on at least one root tongue of each blade in said transition zone which lug engages the adjacent platform member.

4. A blade and blade mounting assembly according to claim 1 in which each root tongue has a root zone which lies within one of said grooves and a transition zone extending from said root zone to said aerofoil portion, a tubular ferrule extends transversely through the two root tongues of each blade in said transition zone, and at least'one lacing wire extends through said ferrules and said platform members.

References Cited in the file of this patent FOREIGN PATENTS 15,893 Great Britain 1903 59,398 France Jan. 6, 1954 (1st addition to 969,413)

. 131,574 Australia Mar. 1, 1949 701,263 Great Britain Dec. 23, 1953 998,221 France e Sept. 19, 1951